This invention relates to a wireless communication apparatus and method that employ frequency hopping.
In a frequency hopping spread spectrum (FHSS) system, usually a usable frequency band is divided into a plurality of frequency bands (channels) having a fixed bandwidth and the carrier wave of a signal is transmitted while shifting from one channel to another. The particular channels to which a shift is made are given by a hopping pattern (HP). In order to perform communication using the FHSS system, it is required that both the sending and receiving sides have the same hopping pattern and that the system be operated in synchronized fashion. More specifically, demodulation on the receiving side must be performed while changing the reception frequency on the receiving side to follow up the hopping pattern on the sending side. That is, it is required that one and the same hopping pattern be shared by the wireless terminals on the sending and receiving sides in order for communication between the two terminals to be started.
In other words, a wireless terminal possesses only one hopping pattern, which is set when communication starts, and this wireless terminal is capable of communicating only with a specific wireless terminal having the same hopping pattern. Accordingly, in order for a plurality of wireless terminals to communicate with one another simultaneously, communication is carried out by applying time-division multiplexing to communication time based upon the hopping pattern used.
However, a problem arises with this method of communicating. Specifically, when communication time is time-division multiplexed by a single hopping pattern, in the manner mentioned above, in a scenario in which a plurality of wireless terminals communicate simultaneously, this hopping pattern is shared in communication with the other wireless terminals in time-division multiplexing. This means that one wireless terminal cannot communicate simultaneously with these wireless terminals and with another new wireless terminal outside this group.
Further, methods of changing over frequency in conventional wireless communication using frequency hopping include a method of switching frequency every communication frame in accordance with the hopping pattern and a method of switching frequency during the course of a communication frame.
When communication is performed, regardless of the frequency switching method, a communication frame is assembled by adding identification information such as the system ID or individual ID onto the beginning of the communication information and then transmitting the assembled communication frame. The receiving side analyzes the identification information of the received communication frame and accepts the ensuing communication information only if the identification information matches that of the receiving apparatus.
Further, in voice communication, transmission of audio information must be performed in continuous fashion owing to the need for real-time communication. In data communication, however, data cannot be transmitted continuously. In other words, data are transmitted at such time that the data are generated.
Accordingly, another system installed in the neighborhood of one's own apparatus is capable of performing data communication even it is communicating data with this apparatus by using the same hopping pattern. However, another wireless communication apparatus will not recognize the fact that the neighborhood system is communicating using the identical hopping pattern or a hopping pattern in which frequencies are superposed.
Further, with the method of switching frequency in the middle of a communication frame, identification information cannot be added onto all frequencies to which a changeover is made. This means that if an apparatus should happen to receive data transmitted from a system installed in the neighborhood, these data will be received accidentally as data transmitted to that apparatus.